Abstract: V838 Monocerotis is a unique erupting variable star that is producing a spectacular light echo. The nature of its outburst, in which the star expanded rapidly to become an extremely cool supergiant and temporarily one of the brightest stars in the Milky Way, remains unexplained; it is one of the leading current challenges to our understanding of stellar evolution. Using the 1.5m SMARTS/CTIO telescope, we have discovered three B-type stars within 1 arcmin of V838 Mon, and the variable itself has an unresolved B companion. Thus V838 Mon lies within a young cluster of about Pleiades age, in spite of its location ~6 kpc away in the rough direction of the Galactic anticenter. Using WIYN and the multi-object Hydra spectrograph, we propose to obtain spectra of several dozen stars within a few arcmin of V838 Mon, in order to identify cluster members and reject stars belonging to the rich stellar foreground in this low-latitude field. Specific goals are (a) to determine the turnoff mass and age of the cluster, and (b) to refine the distance through main-sequence fitting. Both pieces of information will help constrain explanations for the outburst mechanism. NOTE: we received 2 WIYN nights for this program in 2006A, but only got ~4 hours of underexposed data through clouds.